Supplementary Material for: Evaluation of Stuttering in Multilingual Speakers: A Systematic Review of Diagnostic Recommendations

Introduction
There is no definitive, comprehensive guide for diagnosing stuttering in multilingual speakers, and research suggests that monolingual-based diagnostic criteria may lead to misidentification in this population. This systematic review aimed to identify and consolidate conventional diagnostic guidelines for multilingual speakers and evaluate their validity in light of empirical evidence on stuttering and multilingualism.

Method
A systematic review was conducted using PubMed, Science Direct, SAGE, CINAHL, and Google Scholar using specific MESH terms (e.g., “stuttering”, “multilingual”, “bilingual”, “bilingualism”, “assessment”, “diagnosis”). No limits were placed on the years of publication. A hand search of the bibliography of articles that met the criteria was also performed to identify articles that were not found by the database search.

Results
After removing duplicates and applying the exclusion and inclusion criteria, 53 articles remained. Recommendations were related to the nature of speech disfluencies (e.g., evaluate types and frequencies of stuttering behaviors and associated behaviors such as excessive muscular tension and physical concomitants in all languages spoken), diagnostic procedures (e.g., consider case history; language history, proficiency, and dominance), and supplementary data (e.g., use standardized assessments designed for bilinguals).

Conclusion
Collectively, findings support a holistic approach that considers current knowledge about multilingual language development, speech patterns, and broader speaker characteristics beyond disfluencies. In particular, there was an overwhelming consensus that stuttering should be evaluated in all languages spoken, and that the presence of dysrhythmic phonation (i.e., blocks and prolongations) and associated behaviors such as excessive tension and physical concomitants (e.g., eye twitching, facial grimacing, head jerks) increase diagnostic accuracy. Results also highlight the need for comprehensive, validated guidelines, and dynamic assessments to augment standardized evaluation for multilingual speakers.